The invention relates to circuitry for rapid charging of a battery or accumulator with a pulsating current derived from supply mains. An electronic switch is used in the charge circuit to switch on the charging current by means of a control electrode and to block the charge current when the voltage of the accumulator corresponds to an adjustable reference voltage.
In previously known charging circuits of this kind, the electronic switch in the charge circuit of the accumulator is formed as a thyristor having a control electrode connected to a voltage divider connected in parallel with a pulsating charge voltage. The cathode of the thyristor is connected to the positive pole of the accumulator, and the voltage divider is designed so that the voltage present on the control electrode of the thyristor is larger than the eventual desired voltage on the accumulator by the amount of the ignition voltage of the thyristor. The thyristor is then ignited because of the voltage provided by the voltage divider on the control electrode for each phase of the pulsating charge voltage. When the charge voltage of the accumulator reaches the ideal charge voltage, the difference between the control electrode potential and the cathode potential of the thyristor is no longer large enough to ignite the thyristor, and the charging of the accumulator terminates. One example of a circuit of this general nature is disclosed in my U.S. patent application Ser. No. 531,752, filed Dec. 11, 1974 (now abandoned) and in the corresponding German published specification (Offenlegungsschrift) No. 23 64 326.
Such a known circuit arrangement works satisfactorily for medium-size charge currents lying within the power range of thyristors requiring relatively small control currents. The voltage divider can then be dimensioned so that transverse currents flowing through it are very small relative to the charge current. Relatively large charge currents require thyristors of higher power and necessitate higher control circuit currents. Such large charge currents cannot be accommodated with a simple charge circuit, and increased expense must be incurred to achieve accurate charging of the accumulator to the desired voltage.
Another disadvantage of such a known circuit is that voltage fluctuations in the supply mains cause relatively high charge-current fluctuations, which can amount up to 30% for ordinary supply main voltage fluctuations of 10%. This causes substantial problems, because the magnitude of the charge current affects the voltage reached at the termination of the charge when the charge circuit switches off, and such large charge current variations can terminate the charging before the ideal voltage of the accumulator has been reached. If the mean charge current is made relatively low to avoid excessive charge currents in response to voltage fluctuations in the supply mains, an ordinary voltage drop in the supply mains can considerably reduce the charge current so that the voltage on the accumulator cannot reach the ideal, the charge circuit does not switch off, and the accumulator remains connected to the mains until it is thermally destroyed.
Another disadvantage of prior art circuits of this type is that the charge current cannot be selected to be very high because of the increased charge current that flows at the beginning of the charging operation with the accumulator fully discharged.
The invention involves recognition of the problems in prior art charging circuitry and proposes an improved charging circuit of this type that is simple, inexpensive, and reliable and able to accommodate high charge currents and normal voltage fluctuation in supply mains while maintaining the accuracy of the charge placed on the accumulator without endangering the accumulator or other circuit components.